Taxonomic Hierarchy

Common Name (Official / AAS)

Other Common Names

Cupboard Spider, False Button Spider, Cobweb Spider

Author

Author of species name: Carl Ludwig Koch. First year published: 1838, as Theridion grossum.

Pronunciation

stee-uh-TOE-duh GROW-sah

Meaning

Steatoda literally means “tallowy” in latinized Greek, but it is assumed that Sundevall was going for something more like “rotund or globose” (Cameron 2005). In Latin, the species name grossa translates to “big, thick; such as an unripe fig,” presumably referring to the large, swollen abdomen of the adult females.

Notable Previous Names

Teutana grossa

Identifying Traits of Steatoda grossa

Size

Female Primary Colors

Male Primary Colors

Eyes

Total of eight eyes. When viewed from the front, arranged in two horizontal rows of four (a pattern typical of cobweb spiders in the family Theridiidae). Both rows slightly procurved. The secondary eyes can appear white or silver because of a light-reflecting, crystalline structure inside them called a “tapetum.” In spiders, the anterior median eyes are considered the primary eyes, all others are considered “secondary.” Note: in genus Steatoda (the “false widows”), the lateral eyes are touching each other; in genus Latrodectus (the real “widows”), the lateral eyes are well separated.

Legs

Legs quite long and thin; very smooth and shiny looking (covered in hairs, but those are not visible without a very close examination). The legs are all one color: dark brown or black in the females, light brown or reddish in the adult males.

Body

In females, abdomen is usually purplish-brown with pale markings, though the adults eventually turn completely dark-colored (sometimes all black) which causes them to be mistaken for real black widows. Abdomen is a fat oval and can get very large when the spider is gravid or has just eaten a large meal; the cephalothorax is quite small in relation to the large abdomen and is a uniformly dark color (same color as legs). Note that what distinguishes this spider from a real black widow of the genus Latrodectus is the lack of a red or orange hourglass-shaped marking on the underside of its abdomen.

In adult males, the abdomen is much smaller and more slender than the female; cephalothorax is about equal in size to abdomen. The abdomen of the adult male has a base color of dark brown and retains white or cream-colored markings, which include a crescent-shaped band across the front of the abdomen and a series of triangles and bars further back. Carapace is a reddish brown color.

Range of Steatoda grossa

Steatoda grossa can be found in the following states, provinces and territories across the United States and Canada. Our current understanding of each spider's distribution is drawn from numerous scientific publications and online spider submissions, in order to be as accurate as possible. It is important to remember that spiders do not adhere to the territorial lines decided on by humans, therefore these ranges are subject to change.

Important Range Notes

This species is cosmopolitan in distribution, although it is presumably endemic (native) to Europe. Since it usually lives in close proximity to humans and can be transported by commerce, it’s possible it might wind up somewhere outside of the North American range we have given here. An experienced arachnologist can help you decide if Steatoda grossa is what you’ve found; there are some look-alikes out there.

Canada

Additional Information

Habitat

Extremely common in man-made buildings but can occasionally be found outdoors in other sheltered spots, such as in wood piles, under rocks and bridges, etc. In buildings, they typically build their webs near the ground, but there are exceptions (e.g. some have been found inside cupboards).

Web

This species builds a tangled, three-dimensional “cobweb” snare. The silk is not sticky but prey easily gets tangled and begins to struggle, which sends vibrations to the spider. Using its two back legs, the spider then “throws” silk around the prey until it can no longer escape or harm its captor, at which point the spider goes in for the venom-injecting bite and then begins to feed.

Season

Adults of both genders (as well as egg sacs) can typically be found at any time of year, in our experience.

Food

Prey is any insect, spider, or other arthropod that becomes entangled in the web. It is possible that this spider is a specialist on “pillbugs” (aka “woodlice”; “roly-polies”), probably because both the spider and the pillbugs usually live near the ground and are both nocturnally active. Pillbugs emit a chemical that deters predators, so the fact that Steatoda grossa has no trouble catching and eating them is interesting. In one study of this species in California, it was found that 84% of their diet was indeed pillbugs, as determined by monitoring the spiders’ webs for prey remains (Barmeyer 1975). Steatoda grossa has also been known to feed on real “black widows” of genus Latrodectus (Archer 1947, Branch 1943, Kaston 1978).

Lifecycle

After mating, the male doesn’t live much longer. His total lifespan is about 12-18 months. The female, in contrast, can live upwards of six years. She produces multiple egg sacs after mating (averaging 2 or 3 every few months until the sperm she is storing is depleted). Each egg sac is rather spherical and 5-12mm in diameter, made of fluffy, white silk. Perfectly visible through the silk are the cream-colored eggs; there may be anywhere from 10 to 250 of them in each egg sac. After the eggs hatch, the spiderlings are white and rubbery (this is true for all spiders). It will be another few weeks, and two molts, before they exit the safety of the egg sac.

Remarks

Remember, this species is frequently mistaken for a real “black widow” of the genus Latrodectus. Real “black widows” have a bright red or orange hourglass-shaped marking on the underside of their abdomen, Steatoda (the “false widows”) do not. Both spiders hang upside down in their web, making it pretty easy to spot the difference. Both kinds are nocturnal, though, so you may need to wait until nighttime to investigate; don’t forget your flashlight! Also: Steatoda, as well as Latrodectus, are extremely timid and non-aggressive.

Pictures of Steatoda grossa (False Black Widow)

General

Female Spiders

Male Spiders

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